The present invention relates to subject moving apparatus and an imaging apparatus, or more specifically, to an imaging apparatus that images a subject within an imaging space and subject moving apparatus that moves the subject into the imaging space in the imaging apparatus.
Imaging apparatus including an X-ray computed tomography (CT) system have subject moving apparatus that moves a subject into an imaging space. The imaging apparatus scans the subject, who is moved into the imaging space by the subject moving apparatus, so as to acquire raw data, and produces an image of the subject.
For example, in the case of the X-ray CT system, a subject is asked to lie down on a cradle included in the subject moving apparatus. Thereafter, the subject moving apparatus moves the cradle into the imaging space. Assuming that, for example, helical scan is performed, while the subject moving apparatus is sliding the cradle within the imaging space, an X-ray tube irradiates X-rays to the subject. An X-ray detector detects X-rays transmitted by the subject so that raw data will be acquired. Herein, the X-ray tube and X-ray detector rotate with the body-axis direction of the subject as an axis of rotation. X-rays are irradiated in directions of views around the subject, and raw data is acquired in each of the directions of views. At this time, the subject moving apparatus senses the position of the cradle and moves the cradle so that the cradle will be located at a position determined with conditions for scanning. The raw data items acquired in the respective directions of views are used to reconstruct a tomographic image of the subject under the conditions of a desired slicing position and slice thickness (refer to, for example, Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 10-314162
In order to detect the position of a cradle on which a subject lies down, for example, a rotary housing is brought into contact with the cradle. A rotary encoder is used to acquire information on the number of rotations made by the rotary housing, whereby the position of the cradle is detected.
However, in order to enlarge a scanning range or shorten a scan time, the moving speed of the cradle is increased and the cradle is moved fast. Therefore, when the rotary encoder is used, a backlash or any other drawback takes place. Accordingly, an error in information on the position of the cradle may become significant. Eventually, since a subject cannot be scanned at a position determined with conditions for scanning, diagnostic efficiency deteriorates.
More particularly, in recent years, a scanning procedure for acquiring raw data while the cradle is not only moved at a certain speed but also accelerated or decelerated has been proposed. In this case, the above drawback becomes outstanding.